Apparatus for encoding/decoding multichannel signal and method thereof

ABSTRACT

Provided is an encoding/decoding apparatus and method of multi-channel signals. The encoding apparatus and method of multi-channel signals may encode phase information of the multi-channel signals using a quantization scheme and a lossless encoding scheme, and the decoding apparatus and method of multi-channel signals may decode the phase information using an inverse-quantization scheme and a lossless decoding scheme.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 12/761,720 filed on Apr. 16, 2010, which is set to issue as U.S.Pat. No. 9,112,591 on Aug. 18, 2015. The disclosures of which areincorporated herein by references in their entireties.

DETAILED EXPLANATION OF THE INVENTION

1. Technical Field of the Invention

One or more embodiments relate to an encoding/decoding apparatus andmethod of multi-channel signals, and more particularly, to an encodingapparatus and method of multi-channel signals that may encode phaseinformation through a quantization scheme and a lossless encodingscheme, and a decoding apparatus and method of multi-channel signalsthat may decode phase information through an inverse-quantization schemeand a lossless decoding scheme.

2. [Prior Art in the Field]

As a method of coding stereo signals, a Parametric Stereo (PS)technology may be used. The PS technology may generate mono-signals bydown-mixing inputted stereo signals, extract a stereo parameterindicating side information for the stereo signals, and code the stereosignals by coding the generated mono signals and the extracted stereoparameter.

In this case, as examples of the stereo parameter, Inter-channelIntensity Difference (IID) or Channel Level Difference (CLD) signifyingan intensity difference between energy levels of at least two channelsignals included in the stereo signals, Inter-channel Coherence (ICC) orInter-channel Correlation (ICC) signifying correlation between twochannel signals based on similarity of wave forms of at least twochannel signals included in the stereo signals, Inter-channel PhaseDifference (IPD) signifying a phase difference between at least twochannel signals included in the stereo signals, Overall Phase Difference(OPD) signifying how a phase difference between at least two channelsignals included in the stereo signals is distributed based onmono-signals, and the like may be given.

SUMMARY

According to an aspect of one or more embodiments, there may be providedan encoding apparatus of multi-channel signals, comprising: a parameterextraction unit to extract a plurality of parameters indicatingcharacteristic relation among a plurality of channels constituting themulti-channel signals; a parameter quantization unit to quantize theplurality of parameters; a parameter encoding unit to encode theplurality of quantized parameters; a mono-signal encoding unit to encodea mono-signal obtained by down-mixing the multi-channel signals; and abitstream generation unit to generate an encoded bitstream for themulti-channel signals using the plurality of encoded parameters and theencoded mono-signal, wherein the plurality of parameters includes aphase parameter, and the parameter encoding unit encodes the quantizedphase parameter using a Huffman coding scheme.

According to an aspect of one or more embodiments, there may be provideda decoding apparatus of multi-channel signals, comprising: a mono-signaldecoding unit to decode, from an encoded bitstream of a multi-channelsignal, a mono-signal corresponding to a down-mixed signal of themulti-channel signal; a parameter decoding unit to decode, from thebitstream, a plurality of parameters indicating a characteristicrelation among a plurality of channels constituting the multi-channelsignals; a parameter estimation unit to estimate an Overall PhaseDifference (OPD) regarding a phase difference between the multi-channelsignals and the decoded mono-signal, using the plurality of decodedparameters; a parameter inverse-quantization unit to inverse-quantizethe decoded parameters and the estimated OPD; and an up-mixing unit toup-mix the mono-signal using the inverse-quantized plurality ofparameters and the inverse-quantized OPD.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of embodiments, taken inconjunction with the accompanying drawings of which:

FIG. 1 is a block diagram illustrating a configuration of an encodingapparatus of multi-channel signals according to an embodiment;

FIG. 2 is a diagram used for describing a concept of encoding parametersby applying a 2D Huffman coding scheme on pairs of parameters includingparameters not having a wrapping property;

FIG. 3 is a diagram used for describing a concept of encoding parametersby applying a 2D Huffman coding scheme on pairs of parameters includingparameters having a wrapping property;

FIG. 4 is a block diagram illustrating a decoding apparatus ofmulti-channel signals according to an embodiment;

FIG. 5 is a flowchart illustrating operations of a parameterinverse-quantization unit of inverse-quantize parameters based on aUnified Speech and Audio Coding (USAC) scheme;

FIGS. 6 and 7 are flowcharts illustrating operations of a parameterinverse quantization unit of inverse-quantizing parameters using aMoving Picture Experts Group (MPEG) Surround lossless coding scheme;

FIG. 8 is a flowchart illustrating operations of a parameter inversequantization unit of inverse-quantizing parameters based on a ParametricStereo (PS) lossless coding scheme.

EFFECTS

According to an embodiment, there is an encoding/decoding apparatus ofmulti-channel signals, which may effectively encode/decode a phaseparameter, thereby reducing a number of bits used for expressing thephase parameter.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to the like elements throughout. Embodiments aredescribed below to explain the present disclosure by referring to thefigures.

FIG. 1 is a block diagram illustrating a configuration of an encodingapparatus 100 of multi-channel signals according to an embodiment.

The encoding apparatus 100 includes a parameter extraction unit 110, aparameter quantization unit 120, a parameter encoding unit 130, adown-mixing unit 140, a mono-signal encoding unit 150, and a bitstreamgeneration unit 160. Hereinafter, functions for each of the abovementioned components will be described.

Here, the multi-channel signals may signify signals of a plurality ofchannels, and each of the plurality of channels included in themulti-channel signals may be referred to as a channel signal.

Also, for convenience of description, it may be assumed that themulti-channel signal inputted in the encoding apparatus 100 is astereo-signal including a left channel signal and a right channelsignal. However, it is well understood to those skilled in the art thatthe encoding apparatus 100 according to an embodiment is limited to thestereo signals, and used in encoding the multi-channel signal.

The parameter extraction unit 110 may extract a plurality of parametersindicating a characteristic relation between the left channel signal andright channel signal included in the stereo signal. The plurality ofparameters may include a Channel Level Difference (CLD), anInter-channel Coherence (ICC), an Inter-channel Phase Difference (IPD),an Overall Phase Difference (OPD), and the like. Here, the IPD and theOPD may be an example of a phase parameter regarding phase informationbetween the left channel signal and the right channel signal.

The parameter quantization unit 120 may quantize the extracted pluralityof parameters, and the parameter encoding unit 130 may encode thequantized plurality of parameters.

In this instance, since the OPD is estimated from other parameters, theparameter encoding unit 120 according to an embodiment may encode onlythe CLD, the ICC, and the IPD from among the extracted plurality ofparameters, and does not encode the OPD. Specifically, the encodingapparatus 100 may reduce a number of bits of a transmitted bitstreamwithout encoding and transmitting the OPD. Further descriptions of theestimation of the OPD will be made with reference to a decodingapparatus 400 of a multi-channel signal of FIG. 4.

According to an embodiment, the parameter quantization unit 120 mayquantize the CLD or the ICC. In this case, the CLD may be quantized into8 levels or 16 levels, and the ICC may be quantized into an 8-level.

Also, according to an embodiment, the parameter quantization unit 120may quantize the phase parameter such as the IPD or the OPD other thanthe CLD and the ICC. In this case, the phase parameter may be quantizedinto an 8-level or a 16-level.

When the CLD or the ICC is quantized by the parameter quantization unit120, the parameter encoding unit 130 may encode the quantized CLDbetween a current frame and a previous frame or a differential value ofthe quantized ICC. Specifically, the parameter encoding unit may encodethe CLD or the ICC using a differential coding scheme.

As an example, when the CLD or the ICC is quantized into an 8-level bythe parameter quantization unit 120, the CLD or the ICC may have adifference range of 15 steps ranging from −7 to 7, and the parameterencoding unit 130 may encode the CLD or the ICC having the differencerange of 15 steps. As another example, when the CLD or the ICC isquantized into a 16-level, the CLD or the ICC may have a differencerange of 31 steps ranging from −15 to 15, and the parameter encodingunit 130 may encode the CLD having a difference range of 31 steps.

When the phase parameter is quantized by the parameter quantization unit120, the parameter encoding unit 130 may encode a differential value ofthe quantized phase parameter between the current frame and the previousframe.

As an example, when the phase parameter is quantized into an 8-level bythe parameter quantization unit 120, the parameter encoding unit 130 mayencode a phase parameter having a differential range of 15 steps. Asanother example, when the phase parameter is quantized into a 16-levelby the parameter quantization unit 120, the parameter encoding unit 130may encode a phase parameter having a differential range of 31 steps.

Since a phase has a wrapping property having a periodicity based on360°, for example, 370° is the same as 10°, a number of bits allocatedto express corresponding phase information may be reduced whenquantizing the phase parameter using the wrapping property.

According to an embodiment, the parameter encoding unit 130 may apply amodulo operation to a differential value of a phase parameter having thewrapping property, so that the differential value may always have apositive value. Thus, the parameter encoding unit 130 may not transmit asign bit provided to the phase parameter, so that a number of bits usedto express the phase parameter may be reduced. Also, when applying themodulo operation to the differential value of the phase parameter havingthe wrapping property, discontinuity between the phase parameters mayoccur due to the wrapping property, so that an entropy of a phaseparameter distribution may be prevented from increasing.

When a phase parameter is quantized into an 8-level by the parameterquantization unit 120, the phase parameter may have a differential rangeranging from 0 to 7, and when a phase parameter is quantized into a16-level by the parameter quantization unit 120, the phase parameter mayhave a differential range ranging from 0 to 15. Table 1 shows an exampleof quantization values of the phase parameter having been quantized intothe 8-level, and Table 2 shows an example of quantization values of thephase parameter having been quantized into the 16-level.

TABLE 1 Index 0 1 2 3 4 5 6 7 Representation level 0 π/4 π/2 3π/4 π 5π/43π/2 7π/4,and

TABLE 2 Index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Represen- 0 π/8 π/43π/8 π/2 5π/8 3π/4 7π/8 π 9π/8 5π/4 11π/8 3π/2 13π/8 7π/4 15π/8. tationlevel

For example, when a phase parameter is an IPD having been quantized intoan 8-level, the parameter encoding unit 130 may operate a differentialvalue of the phase parameter by applying a modulo-8 operation, whichwill be expressed by the following Equation 1.

ΔIPD=(IPD−IPD₁+8)%8  [Equation 1]

Here, IPD represents an IPD value of a current frame, IPD₁ represents anIPD value of a previous frame, ‘%8’ represents a modulo-8 operation, andΔIPD represents a differential value of an IPD obtained through themodulo-8 operation.

Table 3 shows examples of ΔIPD values obtained through the modulo-8operation.

In Table 3, ‘Previous’ corresponds to IPD₁, ‘Current’ corresponds toIPD, ‘Diff.’ corresponds to IPD−IPD₁, and ‘Diff with modulo’ correspondsto ΔIPD, respectively.

TABLE 3 Index Previous Current Diff. Diff with Modulo Case1 4 6 2 (2 +8)%8 = 2 Case2 6 4 −2 (−2 + 8)%8 = 6 Case3 0 7 7 (7 + 8)%8 = 7 Case4 7 0−7 (−7 + 8)%8 = 1 Case1 4 6 2 (2 + 8)%8 = 2 Case2 6 4 −2 (−2 + 8)%8 = 6Case3 0 7 7 (7 + 8)%8 = 7 Case4 7 0 −7 (−7 + 8)%8 = 1

In general, when ‘Diff.’ is 0, the lowest number of bits may beobtained, and when ‘Diff.’ is closer to 0 or 7, the number of bits maybe reduced. Since previous data is slowly changed, ‘0’ may signify nodifference with a previous frame, ‘7’ may signify −1 of a differencewith the previous frame, and ‘1’ may signify 1 of the difference withthe previous frame. Accordingly, when ‘Diff.’ is ‘1’, the highestfrequency may be obtained, so that a smaller number of bits may beallocated.

The parameter encoding unit 130 may encode a difference of a parameterquantized through a lossless encoding scheme. For example, the parameterencoding unit 130 may encode the quantized parameter using a Huffmancoding scheme.

The Huffman coding scheme may be one of entropy coding schemes used inthe lossless encoding scheme, and may be a coding algorithm where a signwith different lengths depending on a generation frequency of a symbolcorresponding to each data is used.

As the Huffman coding scheme, a 1D Huffman coding scheme and a 2DHuffman coding scheme may be used. The 1D Huffman coding scheme maysignify a method of encoding each data regarded as a single symbol, andthe 2D Huffman coding scheme may a method of grouping a plurality ofpieces of data into a plurality of data groups including two pieces ofdata, and encoding the plurality of data groups (i.e. pairs of twopieces of data) regarded as a single symbol.

Specifically, when encoding a plurality of parameters using the 1DHuffman coding scheme, the parameter encoding unit 130 may directlyencode each of the plurality of parameters using the 1D Huffman codingscheme.

As an example, when encoding the CLD or the ICC, the parameter encodingunit 130 may perform the 1D Huffman coding scheme on each of a pluralityof CLD values or a plurality of ICC values, each regarded as a singlesymbol.

As another example, when encoding a phase parameter, the parameterencoding unit 130 may perform the 1D Huffman coding scheme on each of aplurality of phase parameter values, each regarded as a single symbol.

Also, when encoding a plurality of parameters using the 2D Huffmancoding scheme, the parameter encoding unit 130 may perform the 2DHuffman coding scheme on a pair of parameters including two parameters.

When encoding the plurality of parameters using the 2D Huffman codingscheme, a correlation between the two parameters constituting the pairof parameters may be reduced. Also, when encoding the plurality ofparameters using the 2D Huffman coding scheme, a bit rate may be reduceddue to a joint probability of two symbols between the two parametersconstituting the pair of parameters.

Hereinafter, operations of the parameter encoding unit 130 of encoding aparameter using the 2D Huffman coding scheme will be further describedwith reference to FIGS. 2 and 3.

FIG. 2 is a diagram used for describing a concept of encoding parametersby applying the 2D Huffman coding scheme on pairs of parametersincluding parameters not having a wrapping property, such as the CLD orthe ICC.

Here, the pairs of parameters are expressed as (X, Y). Each of X and Ycorrespond to a single parameter. For example, in a case of the CLD,each of X and Y may correspond to a single CLD value.

The parameter encoding unit 130 may perform the 2D Huffman coding schemebased on the following three steps.

First, the parameter encoding unit 130 may change X or Y, so that anabsolute value of X is greater than an absolute value of Y, that is,‘|X|

|Y|’. Since, a pair of symbols of X/Y may have a greater value on anX-axis when satisfying ‘|X|

|Y|’, a degree where data is skewed may increase, resulting in areduction in a bit rate. Accordingly, parameters existing in a secondregion may be moved to a first region, parameters existing in a thirdregion may be moved to a fourth region, parameters existing in a sixthregion may be moved to a fifth region, and parameters existing in aseventh region may be moved to an eighth region, respectively. In thiscase, side information of one bit may be applied to each of pairs of themoved parameters.

Next, the parameter encoding unit 130 may change X or Y, so that a sumof X and Y is less than ‘0’, that is, ‘(X+Y)

0’. When satisfying ‘(X+Y)

0’, a sign of each of X and Y may be changed to enable a generatedsymbol to have a positive value.

In this manner, parameters existing in the fourth region may be moved tothe first region, and parameters existing in the fifth region may bemoved to the eighth region, respectively. In this case, side informationof one bit may be applied to each of pairs of the moved parameters. Apair of (X, Y) where a corresponding region is moved is referred to as(X′, Y′).

Next, the parameter encoding unit 130 may obtain a pair of parametershaving been finally decoded through a Largest Absolute Value (LAV)coding scheme that is performed using a parameter having an LAV fromamong a plurality of parameters. The LAV may be side information usedfor the 2D Huffman coding, and may be transmitted through the Huffmancoding. The LAV may denote a symbol value having the largest absolutevalue corresponding to a frame to be currently encoded, and a codebookof the 2D Huffman coding may be determined based on the LAV.

The LAV may be side information for the 2D Huffman coding, and may beencoded and transmitted through the Huffman coding. The LAV may denote asymbol having the largest absolute symbol value from among symbolscorresponding to the frame to be currently encoded. The parameterencoding unit 130 may determine a codebook of the 2D Huffman codingbased on the LAY.

The LAV coding scheme using the LAV may be a coding method for reducinga size of a table used for the 2D Huffman coding, and each parameter ofthe LAV coding scheme may be expressed as four symbols configured of‘1’, ‘3’, ‘5’, and ‘7’.

In a case of the CLD or the ICC, along with an increase in a differencebetween a CLD value or ICC value of a previous frame and a CLD value orICC value of a current frame, a generation frequency may be reduced.Accordingly, when the LAV is ‘7’, the generation frequency may be thesmallest value. The CLD and the ICC may apply the same Huffman codebook.A syntax regarding the Huffman codebook is illustrated in Table 4.

TABLE 4 const HUFF_LAV_TAB huffLavTab = { {0x0, 0x2, 0x6, 0x7} {1, 2, 3,3} {1, 3, 5, 7} }

Here, {0x0, 0x2, 0x6, 0x7} may denote a codebook, {1, 2, 3, 3} denotes alength of the codebook, and {1, 3, 5, 7} denotes an LAV.

A pair of parameters (X″, Y″) having been finally decoded using the LAVcoding scheme may be obtained through an algorithm illustrated in Table5.

TABLE 5 if((X′+Y′) % 2) { X″ = LAV + (1−X′−Y′) / 2; Y″ = LAV + (1−X′+Y′)/ 2; } else { X″ = (X′+Y′) / 2; Y″ = (X′−Y′) / 2; }

Here, ‘LAV’ denotes the largest absolute value, and ‘% 2’ denotes amodulo-2 operation.

FIG. 3 is a diagram used for describing a concept of encoding parametersby applying the 2D Huffman coding scheme on pairs of parametersincluding parameters having a wrapping property, such as the IPD or theOPD.

In this case, different from the 2D Huffman coding scheme described inFIG. 2, the 2D Huffman coding scheme may perform the following twosteps.

First, the parameter encoding unit 130 may change X and Y, so that anabsolute value of X is greater than an absolute value of Y, that is,‘|X|

|Y|’.

As described above, since a difference of a quantized phase parameteralways has a positive value when applying the modulo-operation to thedifference of the quantized phase parameter, the phase parameter mayexist only in the first region. Accordingly, side information of one bitmay be applied to pairs of parameters where a corresponding region ismoved.

Referring to the pair of parameters (X, Y) where the correspondingregion is moved as (X′, Y′), X′ and Y′ may be obtained based on thefollowing Equation 2.

X′=(X+Y)/2, and

Y′=−(X−Y)/2.  [Equation 2]

Next, the parameter encoding unit may obtain a pair of parameters havingbeen finally encoded through the LAV coding scheme using a parameterhaving an LAV from among a plurality of parameters.

The pair of parameters (X″, Y″) having been finally encoded through theLAV coding scheme may be obtained based on the algorithm illustrated inTable 5 above.

When a phase parameter is encoded by the parameter encoding unit 130, aregion movement may occur once, different from when encoding a parametersuch as the CLD or the ICC. Accordingly, the phase parameter is encodedby the parameter encoding unit 130, a number of transmitted bits may beless than a number of transmitted bits when encoding the parameter suchas the CLD or the ICC.

A distribution of an LAV of the IPD may differ from that of the CLD orthe ICC. When a difference is ‘7’, the IPD may have the greatestgeneration frequency. For example, the IPD may have an LAV distributionas illustrated in Table 6.

TABLE 6 Value 1 3 5 7 symbol 0 1 2 3 symbol freq 208 29 12 381 symbolbit 1.598768 4.441227 5.714246 0.725561

Allocation of a codebook length based on a probability distribution,that is, the Huffman coding scheme may be performed referring to anactual distribution of a symbol and a Huffman codebook length. When theactual distribution and the Huffman codebook length do not match to eachother, an optimal performance may not be obtained. Accordingly, theparameter encoding unit 130 may re-map a symbol, and encode there-mapped symbol, thereby overcoming distribution mismatching. In thiscase, the parameter encoding unit 130 may re-map the symbol based on thefollowing Equation 3.

sym=(sym+3)%4.  [Equation 3]

Here, ‘sym’ denotes a symbol, and ‘%4’ denotes a modulo-4 operation.

A relation between the re-mapped symbol and the Huffman codebook isshown in Table 7.

TABLE 7 Value 1 3 5 7 symbol 0 1 2 3 codebook 10 110 111 0 codebooklength 2 3 3 1 entropy 0.660317 0.138095 0.057143 0.604762

Tables 8 to 10 show a syntax regarding a 1D Huffman coding and a 2DHuffman coding which encode a phase parameter.

TABLE 8 Number Syntax of bits Mnemonic HuffData1D(dataType, diffType,pilotCodingFlag, dataBands){   pgOffset = 0;   if ( diffType ==DIFF_FREQ &&!pilotCodingFlag) {     aHuffData1D[0] =1Dhuff_dec(hcodFirstBand_XXX, bsCodeW); 1 . . . x vlclbf     pgOffset =1;   }   for ( i=pgOffset; i<dataBands; i++ ) {     aHuffData1D[i] =1Dhuff_dec(hcod1D_XXX_YY; bsCodeW); 1 . . . x vlclbf     if (aHuffData1D[i] != 0 && dataType != IPD) {       bsSign; 1 Uimsbf      if ( bsSign ) {         aHuffData1D[i] = −aHuffData1D[i];       }    }   }   return (aHuffData1D); }

TABLE 9 Number Syntax of bits Mnemonic HuffData2DFreqPair(dataType,diffType, pilotCodingFlag, dataBands){   LavIdx = 1Dhuff_dec(hcodLavIdx,bsCodeW); 1 . . . 3 Vlclbf   If(dataType==IPD) LavIdx = (LavIdx+3)%4;  lav = lavTabXXX[LavIdx];   pgOffset = 0;   if ( diffType == DIFF_FREQ&&!pilotCodingFlag) {     aHuffData2D[0] = 1Dhuff_dec(hcodFirstBand_XXX,bsCodeW); 1 . . . x Vlclbf     pgOffset = 1;     escapeCode =hcod2D_XXX_YY_FP_LL_escape;     /* specific escape code belonging tothis Huffman table */     escCntr = 0;     for ( i=pgOffset;i<dataBands; i+=2 ) {       (aTmp[0], aTmp[1]) =      2Dhuff_dec(hcod2D_XXX_YY_FP_LL, bsCodeW); 1 . . . x Vlclbf      if (bsCodeWord != escapeCode ) {         aTmpSym = SymmetryData(aTmp );         aHuffData2D[i] = aTmpSym[0];         aHuffData2D[i+1] =aTmpSym[1];       }       else {         aEscList[escCntr++] = i;      }     }   } }

TABLE 10 Number Syntax of bits Mnemonic SymmetryData(aDataPair,dataType){   sumVal = aDataPair[0] + aDataPair[1];   diffVal =aDataPair[0] − aDataPair[1];   if ( sumVal > lav ) {     aDataPair[0] =(2*lav+1) − sumVal;     aDataPair[1] = − diffVal;   }   else {    aDataPair[0] = sumVal;     aDataPair[1] = diffVal;   }   if (aDataPair[0] + aDataPair[1] != 0 && dataType != IPD) {     bsSymBit[0];1 uimsbf     if ( bsSymBit[0] ) {       aDataPair[0] = − aDataPair[0];      aDataPair[1] = − aDataPair[1];     }   }   if ( aDataPair[0] −aDataPair[1] != 0 ) {     bsSymBit[1]; 1 uimsbf     if ( bsSymBit [1] ){       tmpVal = aDataPair[0];       aDataPair[0] = aDataPair[1];      aDataPair[1] = tmpVal;     }   } }

Also, a method where a table of mapping an LavIdx is defined may beused. The LavIdx denotes a symbol outputted through an actual Huffmandecoding scheme, and lavTabIPD denotes an actual LAV of the symbol. Inthis case, a re-mapping of the symbol may be performed based on Table11.

TABLE 11 LavIdx lavTabIPD[LavIdx] 0 7 1 1 2 3 3 5

The encoding apparatus 100 of multi-channel signals according to anembodiment will be further described with reference to FIG. 1.

The down-mixing unit 140 may down-mix a stereo signal to output a monosignal.

The down-mixing may generate a mono signal of a single channel fromstereo signals of at least two channels, and a number of bits of abitstream generated in an encoding process may be reduced through thedown-mixing. In this instance, the mono signal may be a representativesignal of the stereo signal. Specifically, in the encoding apparatus 100may not encode each of a left channel signal and a right channel signalincluded in the stereo signal, and may encode only the mono signal totransmit the encoded mono signal.

For example, a magnitude of the mono signal may be obtained as anaverage value of magnitudes of the left channel signal and the rightchannel signal, and a phase of the mono signal may be obtained as anaverage value of phases of the left channel signal and the right channelsignal.

The mono signal encoding unit 150 may encode the mono signal outputtedfrom the down-mixing unit 140.

As an example, when the stereo signal is a voice signal, the mono signalencoding unit 120 may encode the mono signal in a Code Excited LinearPrediction (CELP) scheme.

As another example, when the stereo signal is a music signal, the monosignal encoding unit 120 may encode the mono signal using a methodsimilar to an existing Moving Picture Experts Group-2/4 Advanced AudioCoding (MPEG-2/4 AAC) scheme or an existing MPEG layer 3 (mp3).

The bitstream generation unit 160 may generate an encoded bitstream withrespect to the stereo signal using a plurality of encoded parameters orencoded mono signals.

As described above, the encoding apparatus 100 may encode phaseinformation of multi-channel signals through a quantization scheme and alossless encoding scheme, and generate a bitstream including the encodedphase information. Hereinafter, a decoding apparatus of multi-channelsignal according to an embodiment will be described with reference toFIG. 4.

FIG. 4 is a block diagram illustrating a decoding apparatus ofmulti-channel signals according to an embodiment.

The decoding apparatus 400 includes a mono signal decoding unit 410, aparameter decoding unit 420, a parameter inverse quantization unit 430,a parameter estimation unit 440, and an up-mixing unit 450. Hereinafter,functions for each the above-mentioned components will be furtherdescribed.

For convenience of description, it is assumed that a bitstream inputtedto the decoding apparatus 400 is an encoded bitstream of a stereosignal.

The mono signal decoding unit 410 may restore, from the encodedbitstream of the stereo signal, a mono signal, that is, a down-mixedsignal of the multi-channel signal. Specifically, when the mono signalis encoded in a time domain, the mono signal decoding unit 410 maydecode the encoded mono signal in the time domain, and when the monosignal is encoded in a frequency domain, the mono signal decoding unit410 may decode the encoded mono signal in the frequency domain.

The parameter decoding unit 420 may restore, from the encoded bitstreamof the stereo signal, a plurality of parameters indicating acharacteristic relation between a plurality of channels constituting themulti-channel signal. In this instance, the plurality of parameters mayinclude a CLD, an ICC, and an IPD, however, may exclude an OPD.

When the OPD is excluded from the plurality of parameters, the parameterestimation unit 430 may estimate the OPD using a plurality of restoredparameters.

Hereinafter, an operation of the parameter estimation 430 that mayestimate the OPD will be further described. Here, equations describedbelow may be merely an example, and thus a modification of each of theequations is possible, which is well understood by those skilled in theart.

The parameter estimation unit 430 may obtain a first intermediatevariable c using the CLD based on the following Equation 4.

$\begin{matrix}{{c(b)} = {10^{\frac{{CLD}{(b)}}{20}}.}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, b denotes an index of a frequency band. In Equation 4, the firstintermediate variable c may be obtained such that an IID value of aspecific frequency band is divided by 20, and the obtained value isexpressed in an index type of 10. In this instance, using the firstintermediate variable c, a second intermediate variable c₁ and a thirdintermediate variable c₂ may be obtained as shown in Equations 5 and 6.

$\begin{matrix}{{{c_{1}(b)} = \frac{\sqrt{2}}{\sqrt{1 + {c^{2}(b)}}}},{and}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{c_{2}(b)} = {\frac{\sqrt{2}{c(b)}}{\sqrt{1 + {c^{2}(b)}}}.}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Specifically, the third intermediate variable may be obtained bymultiplying the second intermediate variable c₁ by the firstintermediate variable c.

Next, the parameter estimation unit 430 may obtain a first right channelsignal and a first left channel signal using the restored mono signal,the second intermediate variable c₁, and the third intermediate variablec₂. The first right channel signal and the first left channel signal maybe represented by Equations 7 and 8, respectively.

{circumflex over (R)} _(n,k) =c ₁ M _(n,k).  [Equation 7]

Here, n denotes a time slot index, and k denotes a parameter band index.The first right channel signal {circumflex over (R)}_(n,k) may beexpressed as a sum of the second intermediate variable c₁ and therestored mono signal M.

{circumflex over (L)} _(n,k) =c ₂ M _(n,k).  [Equation 8]

Here, the first left channel signal {circumflex over (L)}_(n,k) may beexpressed as a sum of the third intermediate variable c₂ and therestored mono signal M.

In this instance, when an IPD is φ, a first mono signal {circumflex over(M)}_(n,k) may be obtained using the first right channel signal{circumflex over (R)}_(n,k) and the first left channel signal{circumflex over (L)}_(n,k), which is represented by the followingEquation 9.

|{circumflex over (M)} _(n,k)|=√{square root over (|{circumflex over(L)} _(n,k)|² +|{circumflex over (R)} _(n,k)|²−2|{circumflex over (L)}_(n,k) ∥{circumflex over (R)} _(n,k)|cos(π−φ))}  [Equation 9]

Also, using Equations 6 to 9, a fourth intermediate variable p based ona time slot and a parameter band may be obtained by the followingEquation 10.

$\begin{matrix}{p_{n,k} = {\frac{{{\hat{L}}_{n,k}} + {{\hat{R}}_{n,k}} + {{\hat{M}}_{n,k}}}{2}.}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Here, the fourth intermediate variable p may be obtained by dividing, by2, a sum of intensities of the first left channel signal, the firstright channel signal, and the first mono signal. In this instance, whenan OPD value is φ₁, the OPD may be obtained by the following Equation11.

$\begin{matrix}{\phi_{1} = {2{{\arctan \left( \sqrt{\frac{\left( {p_{n,k} - {{\hat{L}}_{n,k}}} \right)\left( {p_{n,k} - {{\hat{M}}_{n,k}}} \right)}{p_{n,k}\left( {p_{n,k} - {{\hat{R}}_{n,k}}} \right)}} \right)}.}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

Also, when a value of a difference between the OPD and the IPD is φ₂, φ₂may be obtained by the following Equation 12.

$\begin{matrix}{\phi_{2} = {2{{\arctan \left( \sqrt{\frac{\left( {p_{n,k} - {{\hat{R}}_{n,k}}} \right)\left( {p_{n,k} - {{\hat{M}}_{n,k}}} \right)}{p_{n,k}\left( {p_{n,k} - {{\hat{L}}_{n,k}}} \right)}} \right)}.}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

The obtained value φ₁ in Equation 11 may denote a phase differencebetween the encoded mono signal and the left channel signal to beup-mixed, and the obtained value φ₂ in Equation 12 may denote a phasedifference between the encoded mono signal and the right channel signalto be up-mixed.

Equations 11 and 12 may be equivalent to the following Equation 13.

$\begin{matrix}{{{OPD}_{left}^{l,m} = {\arctan \left( \frac{c_{2}^{l,m}{\sin \left( {IPD}^{l,m} \right)}}{c_{1}^{l,m} + {c_{2}^{l,m}{\cos \left( {IPD}^{l,m} \right)}}} \right)}}{where}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{{c_{1}^{l,m} = \sqrt{\frac{10^{\frac{{CLD}^{l,m}}{10}}}{1 + 10^{\frac{{CLD}^{l,m}}{10}}}}},{c_{2}^{l,m} = \sqrt{\frac{1}{1 + 10^{\frac{{CLD}^{l,m}}{10}}}}}} & \;\end{matrix}$

Here, l and m denote a sub-band index and a parameter set, respectively.

As described above, the parameter estimation unit 430 may generate, fromthe restored mono signal, the first left channel signal and the firstright channel signal with respect to the left channel signal and theright channel signal, using an IID signifying an intensity differencebetween channels of the stereo signal, and generate, from the first leftchannel signal and the first right channel signal, the first mono signalusing an IPD signifying a phase difference between channels of thestereo signal, and estimate an OPD signifying a phase difference betweenthe restored mono signal and the stereo signal, using the generatedfirst left channel signal, the first right channel signal, and the firstmono signal. The parameter inverse quantization unit 440 mayinverse-quantize the restored parameter and the parameter estimated fromthe restored parameter.

Hereinafter, operations of the parameter inverse quantization unit 440that may inverse-quantize a parameter will be further described withreference to FIGS. 5 to 8.

FIG. 5 is a flowchart illustrating operations of a parameterinverse-quantization unit 440 of inverse-quantize parameters based on aUnified Speech and Audio Coding (USAC) scheme.

In operation 501, the parameter inverse-quantization unit 440 maydetermine whether a type of a parameter is a phase parameter.

In operation 502, when the type of the parameter is different from thephase parameter, the parameter inverse-quantization unit 440 mayinverse-quantize a second parameter other than the phase parameter usingan MPEG Surround lossless coding method.

In operation 503, when the type of the parameter is the phase parameter,the parameter inverse-quantization unit 440 may determine an encodingmode of the phase parameter. More specifically, in operation 503,whether the encoding mode of the phase parameter is a 1D Huffman codingor a 2D Huffman coding may be determined.

In operation 504, when the encoding mode of the phase parameter is the1D Huffman coding based on the determination of operation 503, theparameter inverse-quantization unit 440 may determine dT or dF. The dTmay signify calculating a difference based on quantized phaseinformation of the same band in a previous frame, and the dF may signifycalculating a difference based on quantized phase information of aprevious band of a current frame.

In operation 505, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the dT or the Df determined inoperation 504, and perform a 1D Huffman decoding on the phase parameterbased on the determined Huffman codebook.

In operation 506, the parameter inverse-quantization unit 440 mayperform a modulo operation on a previous phase parameter and a currentphase parameter based on the dT or the Df, and restore a quantized phaseparameter.

In operation 507, when the encoding mode of the phase parameter is the2D Huffman coding based on the determination of operation 503, theparameter inverse-quantization unit 440 may perform an LAV decoding.

In operation 508, the parameter inverse-quantization unit 440 maydetermine the Huffman codebook based on the LAV, and perform a 2DHuffman decoding on the phase parameter based on the determined Huffmancodebook.

In operation 509, the parameter inverse-quantization unit 440 mayrestore information about a relation of magnitude of X and Y decoded bythe 2D Huffman decoding, and rearrange an order of X and Y based on therestored information about the relation of magnitude.

In operation 510, the parameter inverse-quantization unit 440 mayperform a modulo operation on the X and Y where the order is rearranged,and restore the quantized phase parameter.

In operation 511, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized phase parameter restored in operation508, and restore the phase parameter.

FIGS. 6 and 7 are flowcharts illustrating operations of the parameterinverse-quantization unit 440 of inverse-quantizing parameters using anMPEG Surround lossless coding scheme.

In operation 601, the parameter inverse-quantization unit 440 maydetermine whether a type of a parameter is a phase parameter.

In operation 603, when the type of the parameter is the phase parameterbased on the determination of operation 601, the parameterinverse-quantization unit 440 may determine an encoding mode of thephase parameter. Specifically, in operation 603, whether the encodingmode of the phase parameter is a 1D Huffman coding or a 2D Huffmancoding.

In operation 604, when the encoding mode of the phase parameter is the1D Huffman coding based on the determination of operation 603, theparameter inverse-quantization unit 440 may determine dT₁ or dF₁.

In operation 605, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the determined dT₁ or dF₁, andperform a 1D Huffman decoding on the phase parameter based on thedetermined Huffman codebook.

In operation 606, the parameter inverse-quantization unit 440 mayrestore, from a previous parameter and a current phase parameter, aquantized phase parameter through an inverse differential decoding and amodulo operation based on the dT₁ or dF₁.

In operation 607, when the encoding mode is the 2D Huffman coding basedon the determination of operation 603, the parameterinverse-quantization unit 440 may perform an LAV decoding.

In operation 608, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the LAV, and perform a 2D Huffmandecoding on the phase parameter based on the determined Huffmancodebook.

In operation 609, the parameter inverse-quantization unit 440 mayrestore information about a relation of magnitude of X and Y decoded bythe 2D Huffman decoding, and rearrange an order of X and Y based on therestored information about the relation of magnitude of X and Y.

In operation 610, the parameter inverse-quantization unit 440 mayrestore the quantized phase parameter from the X and Y where the orderis rearranged through the inverse differential decoding and the modulooperation.

In operation 611, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized phase parameter restored in operation 606or in operation 610.

In operation 602, when the type of the parameter is different from thephase parameter based on the determination of operation 601, theparameter inverse-quantization unit 440 may inverse-quantize a secondparameter other than the phase parameter.

Hereinafter, operation 602 will be further described with reference toFIG. 7.

In operation 60201, the parameter inverse-quantization unit 440 maydetermine an encoding mode of the second parameter. More specifically,in operation 60201, the parameter inverse-quantization unit 440 maydetermine whether the encoding mode of the second parameter is a 1DHuffman coding or a 2D Huffman coding.

In operation 60202, when the encoding mode of the second parameter isthe 1D Huffman coding based on the determination of operation 60201, theparameter inverse-quantization unit 440 may determine dT₂ or dF₂.

In operation 60203, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the determined dT₂ or dF₂, andperform a 1D Huffman decoding on the second parameter based on thedetermined Huffman codebook.

In operation 60204, the parameter inverse-quantization unit 440 maydecode a sign of a difference between a current second parameter and aprevious second parameter.

In operation 60205, the parameter inverse-quantization unit 440 mayrestore, from the previous second parameter and the current secondparameter, a quantized second parameter through an inverse-differentialdecoding based on the dT₂ or dF₂.

In operation 60206, when the encoding mode of the second parameter isthe 2D Huffman coding based on the determination of operation 60201, theparameter inverse-quantization unit 440 may perform an LAV decoding.

In operation 60207, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the LAV, and perform a 2D Huffmandecoding on the phase parameter based on the determined Huffmancodebook.

In operation 60208, the parameter inverse-quantization unit 440 mayrestore information about a relation of magnitude of X and Y decoded bythe 2D Huffman decoding, and rearrange an order of the X and Y based onthe restored information about the relation of magnitude.

In operation 60209, the parameter inverse-quantization unit 440 maydecode a sign of the X and Y where the order is rearranged.

In operation 60210, the parameter inverse-quantization unit 440 mayrestore, from the X and Y where the order is rearranged, a quantizedsecond parameter through an inverse-differential decoding.

In operation 60211, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized second parameter restored in operation60205 and operation 60210.

In operation 611, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized second parameter restored in operation606 and operation 608, and restore the phase parameter.

FIG. 8 is a flowchart illustrating operations of a parameterinverse-quantization unit of inverse-quantizing parameters based on aParametric Stereo (PS) lossless coding scheme.

In operation 801, the parameter inverse-quantization unit 440 maydetermine whether a type of a parameter is an IPD.

In operation 802, when the type of the parameter is the IPD based on thedetermination of operation 801, the parameter inverse-quantization unit440 may determine dT₁ or dF₁.

In operation 803, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the determined dT₁ or dF₁, andperform a Huffman decoding on the IPD based on the Huffman codebook.

In operation 804, the parameter inverse-quantization unit 440 mayrestore, from a previous IPD and a current IPD, a quantized IPD throughan inverse-differential decoding and a modulo operation based on the dT₁or dF₁.

In operation 805, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized IPD to restore the IPD.

In operation 806, when the type of the parameter is different from theIPD based on the determination of operation 801, the parameterinverse-quantization unit 440 may determine dT₂ or dF₂.

In operation 807, the parameter inverse-quantization unit 440 maydetermine a Huffman codebook based on the dT₂ or dF₂, and perform aHuffman decoding on a second parameter other than the IPD based on thedetermined Huffman codebook.

In operation 808, the parameter inverse-quantization unit 440 may decodea sign of a difference between a current second parameter and a previoussecond parameter.

In operation 809, the parameter inverse-quantization unit 440 mayrestore, from the previous second parameter and the current secondparameter, a quantized second parameter through an inverse-differentialdecoding based on the dT₂ or dF₂.

In operation 810, the parameter inverse-quantization unit 440 mayinverse-quantize the quantized second parameter to restore the secondparameter.

The decoding apparatus 400 of the multi-channel signal according to anembodiment will be further described with reference to FIG. 4.

The up-mixing unit 450 may up-mix the mono signal using the restoredparameters and the estimated OPD.

The up-mixing may generate stereo signals of at least two channels frommono signals of a single channel, and correspond to the down-mixing.Hereinafter, operations of the up-mixing unit 450 that may up-mix themono signal using the CLD, the ICC, the IPD, and the OPD will be furtherdescribed.

When the ICC value is ρ, the up-mixing unit 450 may obtain a first phaseα+β and a second phase α−β using the second and third intermediatevariables c₁ and c₂, as illustrated in the following Equations 14 and15.

$\begin{matrix}{{{\alpha + \beta} = {\frac{1}{2}\arccos \; {\rho \cdot \left( {1 + \frac{c_{1} - c_{2}}{\sqrt{2}}} \right)}}},{and}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack \\{{\alpha - \beta} = {\frac{1}{2}\arccos \; {\rho \cdot {\left( {1 - \frac{c_{1} - c_{2}}{\sqrt{2}}} \right).}}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

Next, when the restored mono signal is M and a de-correlated signal isD, the up-mixing unit 450 may obtain an up-mixed left channel signal andan up-mixed right channel signal, as illustrated in the followingEquations 16 and 17, using the first and second phases, the second andthird intermediate variables c₁ and c₂, φ₁ of the OPD value obtainedfrom Equation 11, and φ₂ of the value obtained from Equation 12.

L′=(M·cos(α+β)+D·sin(α+β))·exp(jφ ₁)·c ₂,  [Equation 16]

and

R′=(M·cos(α−β)−D·sin(α−β))·exp(jφ ₂)·c ₁.  [Equation 17]

Although a few embodiments have been shown and described, it would beappreciated by those skilled in the art that changes may be made inthese embodiments without departing from the principles and spirit ofthe disclosure, the scope of which is defined by the claims and theirequivalents.

What is claimed is:
 1. An apparatus for obtaining parameters for use indecoding a down-mixed mono signal, the apparatus comprises: a processorconfigured: to decode, from a bitstream, a plurality of parameters thatrepresent characteristic relations between channels; and to estimate aparameter that represents a phase difference between one of a leftsignal and a right signal and the down-mixed mono signal, by using thedecoded plurality of parameters, wherein the plurality of parameterscomprises a phase parameter, and the phase parameter is decoded byobtaining an index for a Largest Absolute Value (LAV) from thebitstream, obtaining the LAV for the phase parameter from the index,determining a Huffman Codebook based on the LAV, decoding symbols of thephase parameter based on the determined Huffman codebook, and obtaininga quantized phase parameter from the decoded symbols in consideration ofwrapping property of the phase parameter.
 2. The apparatus of claim 1,wherein the processor is configured to perform a modulo operation on adifference of adjacent quantized phase parameters.
 3. The apparatus ofclaim 1, wherein the phase parameter is an Inter-channel PhaseDifference (IPD).
 4. The apparatus of claim 1, wherein the Huffmancodebook has a data set (LavIdx, LavTabIPD), and the data set includes(0,7), (1,1), (2,3), and (3,5).
 5. An apparatus for generating a stereosignal from a down-mixed mono signal, the apparatus comprising: aprocessor configured: to decode, from a bitstream, the down-mixed monosignal; to decode, from the bitstream, a plurality of parameters thatrepresent characteristic relations between channels; to estimate aparameter that represents a phase difference between one of a leftsignal and a right signal and the down-mixed mono signal, by using thedecoded plurality of parameters; and to up-mix the decoded down-mixedmono signal using the decoded plurality of parameters and the estimatedparameter, wherein the plurality of parameters comprises a phaseparameter, and the phase parameter is decoded by obtaining an index fora Largest Absolute Value (LAV) from the bitstream, obtaining the LAV forthe phase parameter from the index, determining a Huffman Codebook basedon the LAV, decoding symbols of the phase parameter based on thedetermined Huffman codebook, and obtaining a quantized phase parameterfrom the decoded symbols in consideration of wrapping property of thephase parameter.
 6. The apparatus of claim 5, wherein the processor isconfigured to perform a modulo operation on a difference of adjacentquantized phase parameters.
 7. The apparatus of claim 5, wherein thephase parameter is an Inter-channel Phase Difference (IPD).
 8. Theapparatus of claim 5, wherein the Huffman codebook has a data set(LavIdx, LavTabIPD), and the data set includes (0,7), (1,1), (2,3), and(3,5).
 9. An apparatus for decoding a phase parameter, the apparatuscomprising: a processor configured: to obtain an index for a LargestAbsolute Value (LAV) from a bitstream; to obtain the LAV for the phaseparameter from the index; to determine a Huffman Codebook based on theLAV; to decode symbols of the phase parameter based on the determinedHuffman codebook; and to obtain a quantized phase parameter from thedecoded symbols in consideration of a wrapping property of the phaseparameter.
 10. The apparatus of claim 9, wherein the processor isconfigured to perform a modulo operation on a difference of adjacentquantized phase parameters.
 11. The apparatus of claim 9, wherein thephase parameter is an Inter-channel Phase Difference (IPD).
 12. Theapparatus of claim 9, wherein the Huffman codebook has a data set(LavIdx, LavTabIPD), and the data set includes (0,7), (1,1), (2,3), and(3,5).